دانلود کتاب از Stardust تا اولین سلولها – خاستگاه و تکامل زندگی اولیه

The origin of life from non-life on Earth remains an enduring mystery. Its resolution would not only slake our human need to understand this most central of existential concerns but would guide us in our long and expanding search for life beyond Earth. It is challenging to study life’s origin on Earth because it began at least four billion years ago and only left tantalizing geologi­cal traces in the form of microfossils and stromatolites in the oldest rocks. A record of the prebiotic processes is not preserved. However, it seems likely that life on Earth was not the outcome of an isolated event but a cosmic imperative and planetary property that appeared on young Earth. Speculation regarding the precise historical path from inanimate to animate—the identity of the building blocks of life available at particular physical locations on prebiotic Earth together with the chemical structures of possible intermediate stages on the road to life— is being rapidly refined using techniques and data arising from many different scientific dis­ciples. This book chronicles the recent breakthroughs in astrobiology that have contributed to understanding the origin of life from a cosmic perspective.

How life created so much diversity from so little physical matter is remarkable. Darwin immortalized this view of life in the last sentence of The Origin of Species: ‘from so simple a beginning, endless forms most beautiful and most wonderful have been and are being evolved.’ The variety of life on Earth is immense and wondrous. Yet, despite their endless variations, the cells that make up all living things contain just three fundamental components in a symbiotic relationship. Nucleic acids such as RNA and DNA are molecules that encode digital informa­tion and can be copied. Proteins are the catalysts and nanobots that perform crucial tasks for cells. Encapsulating all of this is a plasma membrane made from a semipermeable lipid bilayer that protects the cell’s interior from the outside environment. The intrinsic properties of cells do not come from individual cell components but their collaborative dynamics mediated by sophisticated information systems. In protocells—the precursors of all life—the beginnings of this trinity of molecules appeared stepwise, a collection of self-organized RNA and proteins enclosed by a simple membrane. Side by side, the information system coevolved with the molecules of life. The end product of a long biochemical voyage was the emergence of the first cells capable of identical division. The emergence of these first cells was, quite possibly, the most momentous event in the history of our planet, transforming a sterile world into a living Gaia. This book attempts to reconstruct this long molecular voyage by bringing together new insights from astrobiology regarding how heat-loving microbial life could have started on young Earth.

Early in Earth’s history, both volcanism and impact cratering were ubiquitous processes. Both may have created an environments to transform disparate chemical compounds into liv­ing organisms, providing a suitable habitat for life to evolve. I will begin my narrative with this violent Hadean world, capable of taking the building blocks of life with embedded analog information from meteorite impacts and sparking life. I will discuss the chemical evolution of biomolecules in hydrothermal impact crater basins, the most likely birthplace of life. I will discuss the algorithmic origin of life and how viruses might have played a critical role in pre­biotic synthesis and the emergence of the first cells. I will show why there has been renewed optimism in recent years about the existence of life beyond Earth.